For the extracorporeal treatment of blood and further applications, it is of value to know the value of one or more of the patient's parameters in advance. This knowledge may contribute to setting or controlling the treatment machine in a more appropriate manner. For example, knowing the patient's overhydration before setting the ultrafiltration rate or volume may provide for certain advantages. For instance, patients who are treated at an ultrafiltration rate (UFR) that has been set (too) high are likely to collapse during, e.g., dialysis because of the amount of fluid withdrawn from their vessel system by the treatment. Patients who are treated at an ultrafiltration rate (UFR) that has been set (too) low are likely to unnecessarily spend time at the treatment site (hospital, clinic or even at home bound to the treatment machine), or, worse, to be sent home again without having reduced their overhydration (OH) level to an appropriate extent. Regrettably, actual or to-date values are not always available for the parameters of interest at the beginning of a blood treatment session.